That is so cool...I'm not even sure what I'm looking at...but, it's great.
@The Lions Den has pointed out, CT usually serves some nefarious purpose of concealing a defect(s). Generally, if along the spine, it's a CB tick(s) or if on the wrap, small inconspicuous defect(s). If amateur, it is usually very obvious. If professional, much harder to detect. CgC has noted "pen" marks on wraps that they deem accidental in nature, or writing and not what they would consider marks for the purposes of restoration/concealment. Also, books of this vintage were manufactured when the printing process resulted in a fair amount of color offset, misaligned wraps, poor cuts, etc., thereby resulting in much variation in appearance from copy to copy.